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7 Consequences:  Low-mass galaxies must form stars prior to re- ionization; must contain ancient populations  Sharp drop / cessation of star formation activity after re-ionization, may resume only much later  High-mass galaxies’ oldest populations must be as old as low-mass galaxies’ populations or younger Testable predictions! Redshifts of not (yet?) accessible Dwarf galaxies at those redshifts would be extremely difficult targets anyway  Exploit fossil record in nearby Universe instead  Local Group ideal target since oldest populations resolved and accessible with HST 1. The Earliest Epoch of Star Formation

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21 3. Harrassment and Accretion Can we find evidence for this in the surroundings of massive galaxies in the Local Group? in the massive galaxies of the Local Group themselves?  Structural properties of nearby galaxies  Stellar content and population properties of nearby galaxies (including abundance patterns) ‏  Streams around and within massive galaxies Dwarf galaxies might be considered the few survivors of a once more numerous dark matter “building block” galaxy population.